DESCRIPTION: Occupationally, related low back disorders (LBDs) represent a major occupational health concern. The etiology of this health problem is complex and poorly understood. The proposed study investigates the role of biomechanical job demands and psycho social work characteristics in increasing LBD risk among employees in manual materials handling jobs. Although there is a wealth of knowledge associated with each of these categories of risk factors, there is a dearth of studies that have rigorously investigated both categories of risk factors in the same work environment. Therefore, it is difficult to estimate the contribution of each of these risk categories to the overall risk for occupationally-related LBDs. We hypothesize that both types of risk factors make independent contributions to the risk of LBDs, and that psycho social work characteristics are more likely to increase risk for LBD when biomechanical job demands are moderate to low than when they are high. The proposed study uses a prospective cohort design. It significantly increases the standard of scientific rigor of investigations in this area through: (1) reliable, valid state-of-the art measures of both psycho social work characteristics and biomechanical job demands; (2) assessments of exposure variables at multiple points in time; (3) the use of an array of outcome measures for LBD including a validated, highly quantifiable clinical assessment of low back functional status; and (4) adequate power to formally assess both additive and potential interactive effects of the two categories of risk factors. With adequate quantification of exposures, we will be able to accurately estimate the extent to which exposures (both psycho social and biomechanical) need to be decreased to reduce LBP risk. We will also be able to discern when and under what conditions an intervention to improve the psycho social work environment will be likely to reduce LBP and its associated morbidity.